There needs to be another hierarchy above Product line. This hierarchy may be used as a business unit, or VP roll up. In large organizations multiple people will be using the tool to track their efforts, and not all teams will have the same processes to define goals, or initiatives, etc. so another rollup at the top would enable a grouping at a much higher level organizationally. In large orgs goals for instance most often are different at org levels (SVP, VP, etc) however products may overlap.
Thank you for your idea. This is possible today. Product lines can roll-up to other product lines. You can also customize the product line type to, for example, business unit or company. This allows you to setup a hierarchy with as many levels as you need. For example:
Company (product line type: company)
Business unit (product line type: business unit)
Product line
Product
Product
Product line
Product
Product
Business unit
Product line
Product
This video provides additional guidance on configuring your product hierarchy.